This invention relates to an X-ray image sensor used for industrial and remedial purposes.
In a conventional X-ray image sensor, a fiber optic plate is fitted onto a solid state imaging device, a phosphor layer having a sufficient thickness above 1 millimeter is disposed on the fiber optic plate to prevent the X-rays from transmitting through the fiber optic plate. A phosphor that has the center of its light emission range near 500 nm is used as the material of the phosphor layer.
As described above, the conventional X-ray image sensor comprises the combination of the phosphor having a light emission center near 500 nm with the solid state imaging device that has silicon as a principal material and has a broad spectral sensitivity characteristics with 800 nm as the center. Therefore, a loss of from 30 to 40% occurs due to deviation of the phosphors light emission range and the spectral sensitivity characteristics of the imaging device and this problem is left yet to be solved.